Abstract
The synthesis, crystal structure, and magnetic properties of three new mononuclear complexes [Fe(R-LA)(L1)](BPh4), where R-LA2− is a doubly deprotonated pentadentate Schiff base ligand and L1 is a monodentate benzimidazole or furopyridine ligand, are reported. Ligand- and anion-driven changes in crystal structures and magnetic behavior were investigated in terms of the magnetic susceptibility measurements and theoretical calculations.
Highlights
Spin crossover (SCO) ofoctahedral complexes of iron(III) manifests as spin transition between S = 1/2 and S = 5/2 states [1]
Three density functional theory (DFT) functionals, B3LYP [17,18,19], OPBE [20,21], and TPSSh [22,23], were used to optimize the molecular structures together with the polarized triple-ζ quality basis set def2-TZVP proposed by Ahlrichs and co-workers [24], where “verytightopt” optimization criteria were used in ORCA
The crystal structures were determined by single-crystal X-ray diffraction for all three presented compounds 1a, 2a, and 2b, and these crystallized in triclinic (P-1 for 1a and 2a) and monoclinic (P21 /c for 2b) space groups (Table 1)
Summary
Compounds of the general formula [Fe(LA)(L1B)](BPh4 ) contain photoisomerable ligands L1B = 3-phenylazopyridine or 4-phenylazopyridine [12] These complexes are not very interesting from a magnetic point of view because they exhibit only gradual spin transitions. This changed with the introduction of the shorter aliphatic chain in Schiff base ligands by substitution of the derivatives of bis(3-aminopropyl)amine by N-(2-aminoethyl)-1,3-propanediamine. Inspired by the abovementioned results we decided to attempt preparation of the [Fe(LA)(L1)](BPh4) complexes exhibiting cooperative SCO by using monodentate ligands, which could increase the rigidity and the number of significant non-covalent interactions in the resulting complexes. (L1a) and 1-benzofuro[3,2-c]pyridine (L1b), together with two slightly different pentadentate ligands, H2LA and H23EtO-LA (4-azaheptamethylene-1,7-bis(3-thoxy-salicylideneiminate, Scheme 1).
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